This invention relates in general to devices which utilize a liquid medium to reglect differences in hydrostatic pressure at different elevations, and in particular to such devices which use only one pressure transducer.
The prior art discloses manometer-type instruments which reflect differences of hydrostatic pressure at different elevations being used as levels and relative elevation measuring devices. U.S. Pat. No. 3,577,645 by Zurawski presents an open reservoir of liquid in liquid communication with a leveling head (an elongated open-top glass tube vertically oriented) via a long flexible tube. An adjustable index marker slides vertically along the glass tube. The leveling head is first placed at a reference elevation, and the reservoir is placed at a convenient elevation such that a top of a liquid column in the head is within the sliding range of the index marker which is then aligned therewith. Thereafter, the liquid column in the head will rise above or drop below the index mark whenever the head is at an elevation below or above, respectively, the reference elevation. It is disclosed as being used as a level for installing raised floors.
U.S. Pat. No. 3,117,381 by Durkin presents another manometer-type instrument for measuring land levels, the basic elements being the same as disclosed by Zurawski. U.S. Pat. No, 3,835,548 by Gearhart presents another similar device used as a level for masonry work. U.S. Pat. No. 4,041,613 by Bishop presents a similar device adapted as a level for building and engineering projects.
The previously discussed prior art does not use any pressure transducers and consequently are very limited in their range of measurable elevations for a given reservoir position. U.S. Pat. No. 4,145,817 by Ager presents a long flexible hose filled with a fluid and plugged at both ends by two pressure transducers, each transducer adapted to sense any pressure developed by the fluid at its end of the hose. Both transducers are in electrical communication with a separate control box which indicates the difference in elevation between the ends of the hose. U.S. Pat. No. 4,218,919 by Stephenson, et al., presents an elevation measuring device the basic elements of which are substantially the same as Ager's device.
Both the Ager and the Stephenson devices require two pressure transducers, one at each end of the fluid tube. This has several disadvantages when compared to a single pressure transducer device as presented herein. Firstly, having pressure sensors at both ends complicates manufacturing of the device because transducer power and/or signal writing must parallel the fluid tube and special cicuitry must be added to minimize errors due to signal wire length and differential sensor environment drift. Furthermore, a separate control module in electrical communication with both pressure sensors is required, which further complicates and increases the cost of manufacturing. Secondly, a precision pressure transducer can easily be the single most costly component in such a system, and the inclusion of two transducers can seriously impact the system retail cost. Thirdly, even transducers of identical performance (very costly) can compound system error when located in separate, different and sometimes unpredictable environments, and if the transducers are not performance matched, further errors can be added to those caused by environmental differences and compounded along therewith. Fourthly, the device as disclosed herein is easier to use than any of the prior art.
The device of this invention can be used to great advantage in place of optical levels or transits, because it is much easier to set up and use. Furthermore, this invention can be used through bushes and trees whereas such foilage would impair or prohibit the usefulness of optical levels of transits.
Other advantages and attributes of this invention will be readily discernible upon the reading of the text hereinafter.